Two-level systems driven by large-amplitude fields

Sahel Ashhab, J. R. Johansson, Alexandre M. Zagoskin +1 more

We analyze the dynamics of a two-level system subject to driving by large-amplitude external fields, focusing on the resonance properties in the case of driving around the region of avoided level crossing. In particular, we consider three main questions that characterize resonance dynamics: (1) the resonance condition, (2) the frequency of the resulting oscillations on resonance, and (3) the width of the resonance. We identify the regions of validity of different approximations. In a large region of the parameter space, we use a geometric picture in order to obtain both a simple understanding of the dynamics and quantitative results. The geometric approach is obtained by dividing the evolution into discrete time steps, with each time step described by either a phase shift on the basis states or a coherent mixing process corresponding to a Landau-Zener crossing. We compare the results of the geometric picture with those of a rotating wave approximation. We also comment briefly on the prospects of employing strong driving as a useful tool to manipulate two-level systems.

Z. K. Yankauskas, G. I. Valyukenas

R. N. Shakhmuratov

Qualitative aspects of the polarization locking in phase with the driving field are discussed. It is shown that particles, with a resonant detuning smaller than Rabi frequency, can be preferentially oriented along the driving field amplitude. This direction determines a new quantization axis of the two-level system (TLS) driven by the resonant field. So, the behavior of the driven TLS can be described by a new nondriven TLS which reaches the equilibrium by the interaction with a reservoir or its environment. Eigenstates of the new TLS are symmetric and asymmetric superpositions of the original TLS states.

Frank Großmann

Shunsuke Nishimura, Kohei M. Itoh, Junko Ishi‐Hayase +2 more

The nitrogen-vacancy center (NVC) in a diamond is a promising platform for Floquet engineering. Using the synchronized readout, we investigate the NVC's Floquet state driven by the Carr-Purcell sequence in a large-amplitude ac magnetic field. We observe the dynamics represented as Bessel functions up to 211th order in a systematic and quantitative agreement with the theoretical model. Furthermore, numerical calculations show that the effect of finite pulse duration and error limits the modulation amplitude available for Floquet engineering. This work provides an approach to precisely investigate Floquet engineering, showing the extendable range of modulation amplitude for two-level systems.